The increase in water temperatures has been identified as a significant factor causing the bleaching of table coral off the Izu Peninsula of Shizuoka Prefecture in Japan. This rise in ocean temperatures has become a concerning trend, with the water temperatures in waters near the Japanese archipelago hitting record highs from June to February for the third year in a row, affecting the fisheries and aquaculture industries. The Japan Meteorological Agency has highlighted that this three-year streak of record high temperatures is the first time such a phenomenon has been observed since they began monitoring surface sea temperatures in 1982.
In 2023, the average ocean surface temperatures in waters near Japan were notably higher than normal across different periods. For June to August, the temperature was 1 degree higher than the 30-year average from 1991 to 2020. Similarly, during the September-November and December-February periods, the water temperatures were 1.9 degrees and 1.1 degrees higher, respectively. These anomalies in ocean temperatures are impacting marine life and the fishing industry, as seen in the changes in fish distribution and catches reported in different regions of Japan.
The higher temperatures are linked to global warming and a shift in ocean currents, particularly the Black Current, which usually flows eastward away from Japan after reaching the Boso Peninsula. However, since spring 2023, the Black Current has been flowing along the coast of the northeastern Tohoku region, bringing different fish species to the area. This shift in ocean current patterns has led to unexpected catches of fish species not typically found in these regions, indicating the profound impact of changing ocean temperatures on marine ecosystems. Additionally, the Fisheries Agency has noted that the rise in water temperatures is affecting not only fish populations but also the growth of seaweed, which thrives in colder waters, highlighting the broader ecological consequences of the warming oceans on the marine environment.